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mopar mpi

Ron84cj

Ron84cj

Engine nerd
Lifetime Member
City
West Bend
State
WI
Wow, I can't believe I'm admitting this. I've always been a hard core carb guy and I'm seriously considering going efi, the mopar mpi in particular. I don't really consider tbi an upgrade. It's still feeding the middle cylinders more than the outer ones. Which I think is why the mopar kit makes more power and gets better gas mileage (or at least part of the reason).

But I have a few questions. For one, why does it require you to use 92 octane? Or can you run 87 octane and the computer just backs off on the timing only causing a few hp? That I can live with. I really don't want to have to run 92 octane. I know it's based off the 94-95 system, but I thought those ran 87? I know the system will get better gas mileage but if I HAVE TO run the more expensive gas, I'm not really money ahead.

The stock motor is only like 9.2:1 compression. I just rebuilt mine and I have 9:1 compression. So it's a little less but is it enough to cause problems?

I also have read that the kit doesn't like mods to the engine. Mine is stock but with an rv cam in it. I don't remember the specs at the moment but I do know it is very mild. Is this going to cause problems? Shouldn't the computer be able to compensate for these things? I always thought that's what the 02 sensor helped with. I don't know if this makes a difference or not but the rest of my jeep is pretty mild. It's just a fun summer toy that I don't go wheeling with. I do go on trips often so that's why I'm concerned with fuel and mileage. I don't live in the mountains so no elevation issues for me, good ol Wisconsin. I'm only running 31' tires with an ax15 and 3.73 gears.

Sorry if these questions have come up but I need to really make sure I have a full understanding of this kit before I make a very expensive mistake! I hope this all made sense, it's 2 in the morning and I'm really tired. Thanks guys:wave:
 
I run 87 octane in my red Scrambler, 4.2 with the Mopar MPI, no pinging or other problems:thumbsup:

I think the 4.2 head design causes some problems for some people so they recommend the higher octane to avoid pinging:shrug::twocents:

Not sure on the cam, call Hesco, they can help you out:thumbsup:
 
i cant mine will ping on 91 octane which is what we get here and if there is ethanol init you get vapor lock sometimes at least i andseveral friends do... one guy has given up and is swapping in a chevy i've talked to a shop who has installed numerous and got 'some do some dont' and that if you can fool the cps you can retard the timing some but didnt know how...they recommmended trial and error hesco suggest buying their hp computer a buddy did but that made it worse and hesco came back with a custom computer cha ching! we are all at 7000 ft and low humidity and have the 4.0l head, to eliminate pinging, as well. l have an auto trans while the rest are manuals i get 15 16mpg at 60mph power was disappointing as well. the manual trans guys are happy though with the power afaik

knowing what i know now id be hard pressed to do it again
 
I run 87 in mine. No issues. The mpi system won't care about an RV cam. The 91-95 mpi system is very basic and can easily deal with mods all you need to do is go up in injector size.
 
I went with the Mopar Fuel Injection last year on my remanufactured 258. I don't remember my cam specs right now, but it is a slight RV cam. I run 87 Octane and have never had any pinging. I LOVE THE MOPAR FUEL INJECTION!
 
i finally win a lottery and its the disappointing 4.0l head efi conversion
 
scramfan01 said:
I went with the Mopar Fuel Injection last year on my remanufactured 258. I don't remember my cam specs right now, but it is a slight RV cam. I run 87 Octane and have never had any pinging. I LOVE THE MOPAR FUEL INJECTION!
Click to expand...

I just called Hesko and they said the same thing. The kit wont care about an rv cam. They did say that I MIGHT have pinging issues and to correct this I would either have to run premium or switch to the 4.0L head. But it looks like a lot of guys are getting by just fine with 87. If I only have to run premium when I'm on a trip somewhere at high elevation, that's fine with me!

So I called my dealer and from what they tell me this kit is no longer made and there's only 2 left in the country! So I'm waiting on them to call me back to see if they can get one of them. My wife works there and I can get an employee discount.
 
Good luck with the purchase. I hope you get one. Like I said, I have never ran 92 octane in mine, and have never had any pinging. I think yours will be fine.
 
dont count on the 4.0l head fixing any pinging problems still worth doing i thnk but it doesnt necessarily fix the pinging if you have them...
 
Can you move that pick up on the bracket a little bit(to retard the timing) or is it on a solid fixed position?
 
not sure ill have to check agan, im not sure how to maintain alignment and gap if i have to modify the mount i guess i should take it apart and see if a new one can be crafted to work i wonder how much change and which direction it needs to move further in the direction of rotation?
 
If you move the crank sensor pick up in the same direction as the motor turns, then you have retarded the timing. If you measure the balancer and do the math, then you can find out how many inches per degree. That's how you resolve a perpetual pinging engine.
 
ahhhh got it thats really straightforward thanks l suppose its trial and error at that point as to how much to retard it
 
Yea kinda. It all depends on how bad it pings really. I'd say an intermittent ping would need 2 degrees to start with. Persistent pinging would probably require 4-6 degrees.
 
Ok, all I can say is wow. I called my dealer and they aren't able to get either one. They told me walk in price is $2,200 and with my employee discount it would have been about $1,100. I asked if it's really marked up THAT much? He said yes and apparently they were already done with back in 2007:banghead:. Hesko told me they bought the last of them and are limited in numbers. They sell them for $2,680. What a kick in the nuts. I've really got to think about this. That's a lot of money!
 
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